⬅ Doubly Circular Linked List | Code Tutorial

A no-bs line-by-line code explanation of the legendary Doubly Circular Linked List.

public class DoublyCircularLinkedList {

	//Declarations are the same!
	static DNode root;
	static DNode current;
	static DNode temp;
	
	public void addDNode(int data){
		
		DNode dNode = new DNode(data);	
		
		if(root==null){
		
			root = dNode;
			//previous and next were null - now 'root'
			root.nextDNode = root;
			root.previousDNode = root;
			
		}else{
			
			current = root;
			
			//root was equal to null - now it's root.
			while(current.nextDNode!=root){
				
				current = current.nextDNode;
				
			}
			
			//previous
			/*
			current.nextNode = dNode;
			dNode.previousNode = current;
			dNode.nextNode = null; 
			 */
			
			//New
			current.nextDNode = dNode;
			dNode.nextDNode = root;
			dNode.previousDNode = current;
			root.previousDNode = dNode;
			
		}
		
	}
	
	//remains the same! largely because no roots were used
	public void insertDNode(int data,int after){
		
		DNode dNode = new DNode(data);
		int ithDNode = 1;
		current = root;
		
		while(ithDNode != after){
			
			current = current.nextDNode;
			ithDNode++;
			
		}
		
		temp = current.nextDNode;
		
		current.nextDNode = dNode;
		dNode.nextDNode = temp;
		temp.previousDNode = dNode;
		dNode.previousDNode = current;
		
	}
	
	public void deleteDNode(int DNodeNumber){
		
		int ithDNode = 1;
		current = root;
		
		
		if(DNodeNumber == 1){
		
			//previous
			/*
			 * 	root = current.nextNode;
				current.nextNode = null;
				current.previousNode = null;
			 */
			
			//new
			root.nextDNode.previousDNode = root.previousDNode;
			root.previousDNode.nextDNode = root.nextDNode;
			root = root.nextDNode;
		
		}else{
			
			while(ithDNode != DNodeNumber){
				
				current = current.nextDNode;
				ithDNode++;
				
			}
			
			//previous
			/*
			if(current.nextNode == null){
				
				current.previousNode.nextNode = null;
				current.previousNode = null;
				
			}else{
				
				current.previousNode.nextNode = current.nextNode;
				current.nextNode.previousNode = current.previousNode;
				
			}
			 */
			
			//new
			current.nextDNode.previousDNode = current.previousDNode;
			current.previousDNode.nextDNode = current.nextDNode;
			current = current.nextDNode;
		
		}
		
		//add this, you always forget!
		DNode.noOfDLinkedList--;
		
	}
	
	//a bunch of print functions!
	public void print(){
		
		current = root;
		boolean arrow = true;
		
		do{
			
			System.out.print((arrow) ? "|" + current.data + "|" : " --> " + "|" + current.data + "|" );
			
			arrow = false;	
			
			current = current.nextDNode;
			
		}while(current!=root);
		
	}
	
	public void printBackwards(){
		
		current = root;
		boolean arrow = true;
		
		do{
			
			current = current.nextDNode;
			
		}while(current.nextDNode!=root);
		
		do{
			
			System.out.print((arrow) ? "|" + current.data + "|" : " --> " + "|" + current.data + "|" );
			
			arrow = false;	
			
			current = current.previousDNode;
			
		}while(current!=root);
		
		System.out.print(" --> " + "|" + current.data + "|" );
		
	}
	
	public void printCont() {

		current = root;
		boolean arrow = true;
			
		for(int i = 0; i < 15; i++){
				
			System.out.print((arrow) ? "|" + current.data + "|" : " --> " + "|" + current.data + "|" );
				
			arrow = false;	
					
			current = current.nextDNode;
				
		}
			
	}
	
	public void printContBackwards() {

		current = root.previousDNode;
		boolean arrow = true;
			
		for(int i = 0; i < 15; i++){
				
			System.out.print((arrow) ? "|" + current.data + "|" : " --> " + "|" + current.data + "|" );
				
			arrow = false;	
					
			current = current.previousDNode;
				
		}
			
	}
	
	public static void main(String[] args){		
		
		DoublyCircularLinkedList list = new DoublyCircularLinkedList();
		
		list.addDNode(1);
		list.addDNode(2);
		list.addDNode(3);
		list.addDNode(4);
		list.addDNode(5);
		list.addDNode(6);
		
		list.print();
		System.out.println();
		list.printBackwards();
		System.out.println();
		list.printCont();
		System.out.println();
		list.printContBackwards();
		
		System.out.println();
		System.out.println("The number of DNodes in the Linked List is " + DNode.noOfDLinkedList);
		
	}

	

}


public class DNode {

	static int noOfDLinkedList = 0;
	int data;
	DNode nextDNode;
	DNode previousDNode;
	
	DNode(int data){
		
		this.data = data;
		noOfDLinkedList++;
		
	}
	
}